Curing agent for epoxy resins

ABSTRACT

Epoxides and acrylonitrile react with spiroacetal diamines of the formula TO FORM A VISCOUS LIQUID WHICH IS A GOOD HARDENER FOR EPOXY RESIN INTERMEDIATES, IN THE FORMULA R being hydrogen, methyl, or ethyl, and R&#39;&#39; being alkyl having one to six carbon atoms. Epoxy resins cured by means of the hardener are flexible, colorless and transparent.

United States Patent Yoshimura et al.

[451 July 25, 1972 CURING AGENT FOR EPOXY RESINS Inventors: lppei Yoshimura, Tokyo; Norihiko Fukue; Hiroshi Sakamoto, both of Kawasaki-shi; Hisashi Murofushi, Tokyo; Takami Hiyama; Takao Matsunaga, both of Yokohama-shi, all of Japan Assignee: Ajinomoto Co., Inc., Tokyo, Japan Filed: Nov. 26, 1969 Appl. No.: 880,356

Related U.S. Application Data Continuation-impart of Ser. No. 560,067, June 24, 1966, abandoned.

Foreign Application Priority Data June 26, 1965 Japan ..40/38l75 Feb. 9, 1966 Japan ..41/7496 References Cited UNITED STATES PATENTS 4/1964 McGary et a1 ..260/2 OTHER PUBLICATIONS Merten et al.. Chemical Abstracts," Vol. 60 (1964), Col. 571 lh Primary Examiner-Alex Mazel Assistant Examin0r.lames H. Turnipseed Arrorney-Kelman and Herman [57] ABSTRACT Epoxides and acrylonitrile react with spiroacetal diamines of the formula to form a viscous liquid which is a good hardener for epoxy resin intermediates, in the formula R being hydrogen, methyl, or ethyl, and R being alkyl having one to six carbon atoms. Epoxy resins cured by means of the hardener are flexible, colorless and transparent.

2 Claims, No Drawings CURING AGENT FOR EPOXY RESINS This application is a continuation-in-part of our copending application, Ser. No. 560,067, filed June 24, 1966, and now abandoned.

This invention relates to epoxy resin compositions, and particularly to curing agents effective for curing such compositions at room temperature.

Polyamines, acid anhydrides, polyamides and polysulfides have been used commercially heretofore as curing agents in epoxy resin compositions. The flexibility often required of the cured epoxy resin in coatings, adhesives and castings could be achieved by the use of polyamide and polysulfide curing agents, but only at the cost of reduced tensile and flexural strength in the cured resins Moreover, full curing by means of these agents could be achieved only at elevated temperature. The cured resins lack run transparency and are not colorless.

We now have found that epoxy resin intermediates can be cured completely at room temperature to colorless and transparent resins having excellent flexibility without loss of mechanical strength by the use of certain modified spiroacetal diamines as curing agents. The curing agents of the invention are reaction products of epoxides or of acrylonitrile with a spiroacetal diamine of the formula wherein R is hydrogen, methyl or ethyl, and R is straight or branched-chain alkyl having one to six carbon atoms.

The curing agents of the invention are stable and do not discolor in storage, during curing or after curing. They produce hard, tough, substantially colorless and transparent cured resins from all epoxy resin intermediates in present commercial use or otherwise available to us.

spiroacetal diamine compounds of the above formula which have been used successfully for preparing the curing agents of the present invention include 3,9-bis(aminomethyl)-2,4,8,l-tetraoxaspiro[5,5]unde cane,

3 ,9-bis( Z-arninoethyl )-2,4,8, 1 0-tetraoxaspiro[ 5,5 ]undecane,

3 ,9-diethyl-3 ,9-bis( Z-aminoethyl )-2,4,8, 1 0-tetraoxaspiro-[ 5,5 ]undecane, 3 ,9-bis( 3-aminopropyl )-2,4,8, 1 0-tetraoxaspiro[ 5,5 ]undecane, 3,9-bis(4-arninobutyl)-2,4,8,l0-tetraoxaspiro[5,5]undecane, 3 ,9-bis( l, l -dimethyl-4-aminobutyl)-2,4,8, l O-tetraoxaspiro- [5,5]undecane,

and the like. The spiroacetal diamine compounds may be prepared by the methods disclosed in the German Pat. No. 1,092,029 or the U.S. Pat. No. 2,996,517 wherein formyl nitrile and pentaerythritol are reacted in the presence of an acid catalyst, and the formed intermediate 3,9-bis(cyanoalkyl)-2,4,8,lO-tetraoxaspiro [5,5]undecane is subjected to catalytic hydrogenation. They may also be prepared by reacting an aminoaldehyde ac'etal with pentaerythritol in the presence of an acid catalyst.

If epoxides are used as adduct components with the spiroacetal diamines, any epoxide having at least one oxirane group in the molecule may be used. Examples of such epoxides are alkyl and alkenyl glycidyl ethets, aryl glycidyl ethers, glycidyl esters, alkylene oxides, alicyclic epoxides, and epoxidized vegetal and animal oils. Representatives of these groups which have been found efiective for the purposes of this invention are listed below, but it will be evident from the varied nature of the listed compounds that many other epoxides may Lil similarly be employed. We are not aware of epoxides not capable of forming adducts with the aforedefined spiroacetal diamine compounds, nor of such adducts which would not be suitable as hardeners for epoxy resin compositions. In the following list, G is glycidyl (l) Alky land AlkenylGlycidylEthers n-Propyl glycidyl ether C H -OG n-Butyl glycidyl ether GH -0G Allyl glycidyl ether Cll), CPL-CH,- G Digl cidyl ether G-O-G Diet yleneglycol diglycidyl ether GO-(CH,CH -O),-G Triethyleneglycol diglycidyl ether GO(CH,CH,-O) ,G Butanediol di lycid lether GO(CH,).OG Glycerine dig? cid ether GO-CH,-CHOHCH,OG Ptillyethyleneg yco diglycidyl GO(CH,CH,O),,OG et er (n being an integer greater than 3) (2) ArylGlycidylEthers Phenyl glycidyl ether CJh-OG Cresyl glycidyl ether Cl-l -,C,H OG

p-Butylphenyl glycidyl ether Is aI CBH4 P-Pentadecylphen I glycidyl ether Diglycidyl ether 0 Bisphenol A wherein n is zero or an integer Digl cidyl ether of resorcinol mycid lphenyl lycidyl ether Digycidy ether 0 diphenolic acr HaCHrC 0 OH Polyglycidyl ether of novolac resin G68-C H.CH (GOC l-I CH ),,C H. Diglycidyl ether of hydroquinone GO-CJL-OG Digl cidyl ether of catechol GO-C H,,-0G )a'- B Tng ycidyl ether of phloroglucinol 3 Glycidyl Esters Cardura E, a commercial product, mainly consisting of glycidyl esters of synthetic tertiary fatty acids,

wherein R,, R R are saturated aliphatic chains, and the total number of carbon atoms in the acid moiety of the molecule is between 9 and l l.

Glycidyl methacr late Glycidyl esters o polymeric fatty lCld R=pol meric fattfy acid radical CH, =C(CH )--COOG G-OCO-ll-COO-G Styrene oxidev Cally-(lll- -Cll1 Butadiene dioxide CII ClICIli-Clh Dimethylpentndieno dioxide .l ClIzC (Clh)ClIaC(C1l3)--Clh Divinylbonzene dioxide A. oin--on--c.in-on-- on.

6 Alie elic epoxides Vinylcycloliexane monoxide... /CQ,

Oil OlIClI::Oll l Cg II: C II Vinyieyclohexime dioxide C3:

0% CH-C;C h O l l 0 a-Pinene oxide CH3 Dipenteno monoxide M CH3 Limonene dioxide C H:

3,4-Epoxy-6-methy1cyclohexy1- methyl 3,4-epoxy-6-methylcyelohexanecarboxylate (6) Epoxidized Oils Epoxidized soybean oils Epoxidized tallow oil Epoxidized lemon oil Epoxidized lanoline oil The curing agents of the invention are prepared by heating a mixture of the spiroacetal diamine with an epoxide or with acrylonitrile with or without a solvent inert to the reactants. Suitable solvents include methanol, ethanol, butanol, benzene, toluene, xylene, dioxane, ethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether and the like. Heating is continued until a homogeneous viscous liquid is obtained after removal of the solvent, if any The reaction temperature is preferably above the melting point of the diamine and below the boiling point of the epoxide or acrylonitrile so that the mixture is liquid. However, temperatures between 20 and 150 C. are usually satisfactory, and the time required varies inversely with the temperature.

It is preferred to use more than 0.25 mole of spiroacetal diamine per oxirane mole equivalent of the epoxide in the reaction mixture or per mole of acrylonitrile, but as much'as 10 moles of spiroacetal diamine may belemployed. A curing agent prepared with less than 0.25 mole spiroacetal diamine per oxirane mole equivalent of the epoxide or per mole of the acrylonitrile does not completely cure an epoxy resin because of inadequate cross-linking, and the partly cured resin has poor chemical and mechanical properties. -.When more than l0 moles of spiroacetal diamine are employed in preparing the Best results are generally obtained with curing agents prepared from 0.5 to 6 mole spiroacetal diamine per oxirane mole equivalent of epoxide or per mole of acrylonitrile.

The curing agents of the invention are colorless and transparent. They do not irritate the skin upon contact. No discoloration of the curing agents has been observed in three months of storage at room temperature. Storage for more than two months at temperatures below 5 C. did not cause the unreacted spiroacetal diamine to crystallize nor otherwise to precipitate.

Representative epoxy resin intermediates capable of being cured by the curing agents of this invention are those based on the glycidyl ethers of polyhydric phenols, such as 2,2-bis(4- hydroxyphenyl)-propane, resorcinol, hydroquinone, pyrocatechol, saligenin, 4,4-diphenylhydroxybiphenyl, 1,5- dihydroxynaphthalene, dihydroxydiphenylmethane, dihydroxydiphenylsulfone, and on the glycidyl ethers of polyhydric a1- cohols, such as ethylene glycol, propylene glycol and glycerin.

The required amount of curing agent is determined by the number of active hydrogen atoms in the curing agent employed, and the number of oxirane groups in the epoxy resin intermediate. In general, it is preferred to use equivalent weights of spiroacetal diamine adducts and epoxy resin intermediates. However, the properties of the cured resin are not significantly affected by variations of not more than percent in the amount of the curing agent.

The epoxy resins cured according to this invention are superior to resins produced from the same intermediates by means of conventional curing agents by a combination of better flexural properties, higher impact resistance, and better thermal shock resistance with equal or superior tensile strength and hardness.

The epoxy resin intermediates can be cured completely at room temperature to colorless and transparent resins having excellent mechanical properties. Heating is unnecessary, but may be resorted to for obtaining maximum strength in a shorter time. Even when cured at elevated temperature, the cured resins are not stained by the curing agents of this inventron.

The curing agents are compatible with all conventional fillers, diluents, reinforcing agents, pigments and other processing agents, such as flow control additives and accelerators, so that resin compositions may be formulated according to the intended application in the usual manner.

The following examples further illustrate the present inven- 45 EXAMPLE 1 In a four-necked flask equipped with a stirrer, a reflux con- 50 denser, a dropping funnel and a thermometer, 109.6 g (0.4 mole) 3,9-bis(3-aminopropyl)-2,4,8,10-tetroxaspiro[5,5]dundecane (hereinafter referred to as ATU) were heated to 45 55 C. To the melt so obtained, 30.0 g (0.2 mole) phenylglycidyl ether were added drop by drop over a period of two hours, and the mixture was kept at the same temperature for one hour longer. A colorless and transparent, viscous, liquid mixture of the reaction product and of unreacted ATU was obtained. When stored below 5 C. for 24 hours and for three months at room temperature, the mixture did not form a precipitate.

The same procedure was used in preparing other curing agents from diamines and epoxides as listed in Table l. Cardura E is a commercially produced glycidyl ester more closely identified above. Epon is a registered Trademark for various phenyl glycidyl ethers of the formula indicated above, all of which form curing agents with the spiroacetal diamines of this ATU Notes: (1) 3.4-epoxy-6-methy1cyc1ohexylmethyl 3,4-epoxy-6-methy1- cyclohexanecarboxylate 2) 3,9-bis( 4-aminobutyl)-2,4,8, l O-tetroxaspirol 5 .5 Icunde'cune 15 (3) 3.9-bis( 2-aminoethyl)-2.4,8,10-tetroxaspirol5,5]cundecune (4) 3,9-bis(2-aminoethy1)-3,9-diethyl-2.4,8,IO-tetroxaspirol5.5lundecane EXAMPLE 2 20' The curing agents listed in Table 1 were mixed with Epon 828 in the weight percentage ratios listed in Table 2 (grams icuring agent per 100 g Epon 828), and'50 g batches of the several mixtures were stored in identical containers in an airconditioned room at 20- 'l C. and 65 percent relative humidity. For comparison, two batches of Epon 828 were mixed with conventional, typical polyamine and polyamide curing agents respectively in the ratios recommended. The polyarnine was triethylene tetramine (TETA), the polyamide curing agent a commercial product whose precise composition is not known (Tohmide 245), and which has an amine value of 400. The pot livesin minutes and maximum exotherms of the mixtures are listed in Table 2.

TABLE 2 :Curing Pot Life, Max.

Agent min. exotherm, C

N0. 1 60% 40 97 2 60 65 61 3 65 103 4 60 68 5 50 55 1 15 6 70 70 46 7 55 70 82 8 85 75 10.55 50 92 11 50 55 103 12 60 71 TETA 10 S0 124 Tohmide 245 50 75 39 EXAMPLE 3 Resin specimens prepared from the batches described in Example 2 were subjected to heat distortion tests (ASTM D648-56) and flexure tests (ASTM D790-63), and the curing 55 conditions and test results are listed in Table 3, wherein R.T. is

room temperature, all other temperatures are in C., and HDT is heat distortion temperature. No failure under the available test conditions is indicated by 60 TABLE 3 Curing Curing Strain Strength Modulus Agent Conditions HDT Max., mm kglmm kg/mm 65 No. 1 nrr. so 31.: 14.4 388 3 hrs/8075 29.2 12.2 298 No. 2 HT. 52 20.0 10.0 290 3 hrs/80 55 10.8 311 No.3 R T 75 11.0 290 3 hrs/8077 29.6 11.0 287 No. 4 R.T. 74 33.7 11.4 292 3 hrs/8065 10.7 309 No. 5 R T. 52 21.0 10.0 295 3hrs/12075 11.5 313 No. 6 R.T. 58 34.2 10.5 320 3 hrs/10055 10.7 310 75 No.7 R.T. 79 28.5 11.2 290 3 hrs/8074 31.7 11.4 296 Test specimens were prepared from 80 g each of compositions listed in Table 2 by curing the mixtures in cylindrical molds of 70 mm diameter and 30 mm depth together with a spring washer of one inch diameter at room temperature for 14 days. They were then tested for thermal shock resistance by up to ten cycles of alternating immersion in boiling water and in ice water for periods of 30 minutes, and inspected. The results are listed in Table 4 in which the ratings have the following meaning:

A No cracks D Considerably cracked B Slight crack E Large and numerous cracks C Small crack Cracked during curing Where more than one line is associated with a curing agent, more than one specimen was tested. No. 7A differed from No. 7 in Table 2 by use of 70 percent curing agent (15 percent excess).

TABLE 4 Number of Cycles Curing Agent 1 2 3 4 5 EXAMPLE 5 machined to test bars mm X 15 mm X 45 mm having a transverse semicylindrical notch of 1 mm radius in the center of one of the elongated rectangular faces. The notched specimens were subjected to Sharpy impact resistance tests according to Japanese Industrial Standard K-69ll. Mean values of six tests are listed in Table 5. The capacity of the apparatus used was 15.7 kg-cm/cm and values of 157+ in the Table indicate that the specimen did not fail. Comparison tests were run with a mixture prepared from Epon 828 and 9 percent TETA cured 14 days at room temperature, and with a mixture of Epon 828 with 50 percent Tohmide 245 cured at 65 C. for 3 hours.

TABLE 5 Curing Agent No. 6 No. 7 No. 4 No. 5 TETA Tohmide lmpact resistance,

kg-cm/cm 14.4 157+ 14.3 15.7-1- 4.3 8.9

8 EXAMPLE 6 The mixtures described in Example 5 were cured in a glass mold at C., for 30 minutes to prepare resin sheets fromv which tensile test specimens were machinedto the specifications of Japanese Industrial Standard K-691 l. The specimens were tested for tensile strength and modulus of elasticity in tension at 21 C., RH. 65 percent, at a cross-head speed of 5 mm/sec. Mean values in kg/mm of the results obtained with three to six specimens are listed in Table 6. i

TABLE 6 Curing Tensile Agent Strength Modulus No.6 7.15 232 N0. 7 6.52 194 No. 4 7.15 235 N0. 5 7.30 216 TETA 5.09 273 Tohmide 245 6.89 237 EXAMPLE 7 53 g Acrylonitrile (1 mole) were added dropwise to 274 g 1 mole) 3,9-bis(3-aminopropyl)-2,4,8,-l O-tetroxaspirolS ,5] undecane in a flask at 45-55 C. over one hour. The mixture was kept at the same temperature for an additional hour with stirring to produce an adduct which was a transparent viscous liquid. Corresponding adducts were also prepared from the same reactants in a different mole ratio and from other 2,4,8,l0-tetroxaspiro[5,5]undecane derivatives differing in their substituents in positions 3 and 9. Table 7 lists the substituents, the mole ratio of diamine to acrylonitrile employed in each reaction, and a number assigned to the adduct or curing agent for further reference hereinbelow TABLE7 Curing Mole Agent 3,9-Substituents Ratio No 13 3,9-bis(3-aminopropy1) 1:1 No 14 3,9-bis(3-aminopropyl) 2:1 No 15 3,9-bis(4-aminobuty1) 1:1 No 16 3,9-bis(2-aminoethyl) 2:1 No 17 3,9-bis(1,1-dimethy1-4-aminobutyl) 1:1 No 18 3,9-diethyl-3,9-bis(Z-aminoethyl) 2:1

EXAMPLE 8 The adducts listed in Table 7; TETA, and Tohmide 245, were added to Epon '828 in amounts listed in Table 8. 500 g Batches of the mixtures were kept at 20xl C. and 65 percent R.H., and they reacted exothermally to form gels. The time to gel (pot life), the maximum exotherm, and the time to reach the maximum temperature were determined and are listed in The curing agents of the invention listed in Table 8 formed gels more slowly than the known agents although the max- A imum exotherm values were nearly the same. This is of particular value in casting compositions.

EXAMPLE 9 Heat distortion and flexure tests were performed on the resins formed according to Example 8 after room temperature curing for the resins of the invention and one batch of TETA- cured resin (TETA A), and after curing at 100 C. for three hours for the TETA-cured resin B, and at 65 C. for three hours for the resin cured with Tohmide 245. The test conditions were as described in Example 3. The resins cured according to this invention had the same color as uncured Epon 828. The conventionally cured resins were yellow or yellowish brown. The test results are listed in Table 9 in the manner of Epon 828 was mixed with ATU (35 percent), adduct No. l (60 percent), No. 2 (60 percent), No. 3 (50 percent), TETA percent) and Tohmide 245 (50 percent). The mixtures so prepared were cured as indicated in Table 10 and subjected to flexure tests under the conditions of Examples 3 and 9. While comparable values for maximum strength and elastic modulus were recorded for the tested resins prepared with curing agents of the invention and ATU alone, the resinscured with t e adducts of the invention were superior in their values of maximum strain before failure to the specimens cured with ATU alone and to those cured with TETA or Tohmide 245 under comparable conditions.

TABLE 10 Curing AGent Curing Conditions Max. Strain, mm

ATU R.T. 19.3 30 min/80 21.8 No. I RS1. 31.3 3 hrs/80 29.7 No. 2 RT. 20.0

3 hrs/80 No. 3 R.T.

3 hrs/80 29.6 TETA R.T. 4.6 3 hrs/100 15.6 Tohmide 245 3 hrs/65 20.7

Epon 828 was chosen in all preceding Examples as the resin intermediate for demonstrating the superior mechanical properties of epoxy resins cured by means of the curing agents of the invention in order to facilitate correlation of the several sets of data. However, closely analogous results were obtained with all other commercially available epoxy resin intermediates which we have been able to test. Epon 828 is merely representative of the glycidyl ethers of bisphenol A, the polycondensation products of the ether, and mixtures thereof, which are useful both as reaction partners for the afore-mentioned spiroacetal diamines in preparing the curing agents, and as resin intermediates which may be hardened by means of the curing agents.

Epon 828 is a liquid mixture of such ethers or ether polycondensation products which has an average molecular weight of approximately 380, a corresponding epoxy equivalent of 185 to 192 g per gram equivalent of epoxide, and an esterification value of about 85. It is prepared by condensation of bisphenol A with epichlorohydrin as generally described in British Patent No. 974,139. The commercially available product has a color of 8 max. (Gardner) and a viscosity of to poises.

Epon 1001, referred to in Table 1, has an average molecular weight of approximately 900 with a corresponding epoxy equivalent of 425-550, and an esterification value of 145. It is a solid melting at 65-75 C., a Gardner color of 4 max., and a viscosity of D-G on the Gardner-Holdt scale as determined in a 40 percent solution of the material in diethyleneglycol monobutyl ether at 25 C.

Epon 834 is a liquid which is intermediate in molecular weight(approximately 480), epoxy equivalent, esterification value and viscosity between the two epoxides described above, and has been used successfully as a reaction partner for the spiroacetal diamines and as a resin intermediate according to this invention.

What is claimed is:

l. A reaction product of a spiroacetal diamine of the formuwherein R is hydrogen, methyl or ethyl, and R is straight or branched alkyl having one to six carbon atoms, with the ratio of said spiroacetal diamine to said acrylonitrile being between 0.25 and 10 moles of said spiroacetal diamine per mole of said acrylonitrile.

2. A product as set forth in claim 1, which is a viscous liquid at 20 C.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 5 797 7 Dated uly 25, 1 2

Inventor) Ippei Yoshimura et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 10, line 46, after "with" insert acrylonitrile Signed and sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents OHM POWSO uscoMM-Dc seam-ps9 \LS. GOViRNMINT HUNTING OIHCI: Illi 'Q-Zii-HA 

2. A product as set forth in claim 1, which is a viscous liquid at 20* C. 